[Choosing Insecticides] Tough Decision?

Editor’s Note: This article is based on Gary Braness’ chapter “Insecticides & Pesticide Safety” from the recently published 10th Edition of the Mallis Handbook of Pest Control. For more information about the new Mallis book, visit www.mallishandbook.com.

The choice of insecticide formulation is often as important as the selection of insecticide active ingredient. When using liquid sprays, pest management professionals may select from formulations like suspension concentrates (SC), wettable powders (WP), capsule suspensions (CS), water dispersible granules (WDG) and emulsifiable concentrates (EC). Insecticide baits have become an important formulation in pest management programs and PMPs may select from various forms of baits including ready-to-use bait stations, gel baits, granular baits and liquid baits. Professionals may also choose to use aerosols, dusts or granular insecticides as part of their management programs. When combined with decisions about selecting the most effective active ingredient, the product choices can be overwhelming even for the most experienced technician. Owners/managers must manage their insecticide inventory to control chemical costs, but at the same time ensure that enough formulations are available for safe and effective management programs. Following is a process based on Integrated Pest Management (IPM) that will aid in the selection of the best formulation(s) for the job.

Before selecting formulations, it is helpful to understand the site(s) to be treated. A complete inspection of the property will provide the information needed to select the best formulation(s) for the job. Carefully consider these 10 questions about formulation selection before making insecticide applications:
 

1. Can the formulation be applied safely in sensitive areas?

Sensitive areas may include food areas of food-handling establishments, hospital or nursing home rooms, classrooms, certain areas at zoos and numerous other sites. Special precautions must be taken in these areas to avoid potential hazards from insecticide application. First, be sure that the product is labeled for use in these areas. Residual sprays may be limited to crack and crevice treatment and may be prohibited from use when rooms are occupied. Select formulations that are low in odor or have no odor and products with low vapor pressure. Bait formulations are often an excellent choice in sensitive areas.
 

2. Will the formulation cause phytotoxicity (plant injury) to plants that are treated?

Phytotoxicity may occur following an insecticide application to plants. It is more likely to occur when using liquid formulations like EC formulations that contain solvents. When plants are to be treated, select formulations that do not contain solvents (e.g., WP, SC, CS formulations). Also, do not treat plants during the hottest parts of the day under direct sunlight. This combination of environmental factors can cause a plant’s foliage to “burn.” Other causes of phytotoxicity may be attributed to using excessive rates, treating sensitive plant varieties, cumulative applications to the same plants and mixtures of products. Manufacturers conduct extensive phytotoxicity trials with their products and can usually provide phytotoxicity information. If in doubt, first try the product on a small sample of plants.

3. Is the formulation effective against the target pest?

Regardless of the pest to be controlled, the objective must be to get the insecticide to the pest. Begin with proper pest identification. You must know if the pest is primarily a flying or crawling insect or if it spends most of its time in or below surfaces. Flying pests may be best controlled with an aerosol formulation. For crawling pests, a residual spray formulation or dust that stays on the surface where pests will contact it may be most appropriate. A bait formulation may be best, especially one that is attractive to the pest and placed in areas where they feed on the bait and ingest a lethal dose of the toxicant. Some active ingredients are selective in their activity against pests, so check the product label to be sure that the pest is listed.
 

4. Will the formulation perform well on the surfaces to be treated?

The interaction of residual insecticide formulations and the surface treated greatly affects insecticide performance. Residual insecticides are applied to a wide variety of surface types. These surfaces can be described as porous, semi-porous or non-porous types. Examples of porous surfaces include: concrete, wooden mulches, unfinished wood, gypsum wallboard, paper and plastics. Common nonporous surfaces are glass, ceramic tile and stainless steel. Semi-porous surfaces such as enamel- and latex-painted wood, vinyl tile and Formica also will be encountered.

Numerous studies have shown that EC formulations are absorbed into porous or semi-porous surfaces and the active ingredients are not available to crawling insect pests. Formulations like WP, SC, CS and D formulations are not easily absorbed by porous surfaces and are more readily “picked up” by crawling insect pests. So, if the target pest is a crawling pest, select formulations that stay on the surface. However, if the target pest is found below surfaces (e.g., wood- boring beetles) an EC formulation is recommended. During the inspection and before application, determine which surface types are most common and identify the target pest(s). Once this information is gathered, you will be able to select the most effective formulation(s).

One of the biggest challenges facing the professional is getting cooperation from the customer to maintain good sanitation practices. In the real world of pest management, many of the surfaces treated are coated with oils, grease, food debris, dust or other organic matter. Many studies have shown that these surface coatings reduce the effectiveness of residual insecticides. Professionals can improve insecticide performance by encouraging their customers to maintain high levels of sanitation.
 

5. How will environmental factors like temperature, humidity, and light affect the formulation?

After insecticides are applied to surfaces, they are subjected to various environmental factors that reduce their effectiveness. High temperatures have been shown to reduce the residual effectiveness of chlorinated hydrocarbon and organophosphate (OP) insecticides. In one study, the combined effects of temperature and humidity for three formulations of an OP (chlorpyrifos) and pyrethroid (cyfluthrin) were evaluated against German cockroaches. The CS formulation of chlorpyrifos was long-lived even when exposed to high temperatures [37°C (99°F)]. However, high temperatures and high humidity decreased residues of chlorpyrifos EC and WP formulations, thereby reducing cockroach mortality. All cyfluthrin formulations were long-lived. This study indicates that high temperature, aging of residues, and selection of insecticide influences cockroach mortality, and that the effect of humidity on cockroach mortality was of less importance. It also showed that residual effectiveness of formulations was correlated with vapor pressures for the insecticides. High temperatures can increase the vapor pressure of insecticides three- to four-fold for each 10°C (50°F) increase in temperature. Generally, insecticides with higher vapor pressures volatilize (e.g., evaporate away from treated surfaces) more rapidly in the same environments than those with lower vapor pressures. The loss of insecticide residue by volatilization is greatest on non-absorbing surfaces. Vapor pressures are known for each active ingredient and may be obtained by reading the Material Safety Data Sheet (MSDS) provided by pesticide manufacturers. Keep in mind, however, that formulation can affect vapor pressures. For example, microencapsulation protects the active ingredient within a polyurea shell, making the active ingredient practically non-volatile.

Other environmental factors such as ultraviolet light may break down insecticides through photodecomposition. Air currents or wind can also reduce the effectiveness of residual insecticides by increasing the rate of volatilization. The effects of environmental factors can be minimized, especially outdoors, if applications are made to cracks and crevices and other protected areas.
 

6. Is the product a cost effective option for the treatment site?

Several factors should be considered when answering this question. First, consider the use rate for the product and then determine the cost of treating a given area (e.g., cost per 1,000 square feet or per home or restaurant). Also, evaluate the time-saving features associated with the use of the product. Savings in labor costs can quickly offset higher insecticide costs. By using this product, can you reduce callbacks? The cost of callbacks is often underestimated. Often, the least expensive product is not the most cost effective.
 

7. Does the formulation mix easily and can it be tank mixed with other pesticides?

Other than ready-to-use products (e.g., baits, dusts, granules and aerosols), professionals must mix the products they use. Some formulations are easier to mix or handle than others. Liquids like EC, SC, and CS formulations are usually preferred over dry formulations such as WPs. However, the use of pre-measured, water-soluble packaging for WP formulations has greatly increased the ease in handling this dry formulation.

Refer to the product label for mixing directions and information about tank mixing. When tank mixing products, follow the most restrictive labeling directions and precautions. Check the label for compatibility with other pesticides. To be sure of physical compatibility, prepare a small sample of the mixture using the proper proportions of water and product.
 

8. Will the formulation run off or drift during the application?

To reduce runoff or drift of insecticides, monitor the weather and avoid adverse conditions such as heavy rain or high wind. Most runoff of pesticides occurs when pesticides are applied to saturated soils or when heavy rains or excess irrigation occur immediately following application. Under high wind conditions, avoid outside spray treatments. Also, lower spray pressure or use a coarse fan nozzle to reduce drift. When conditions are not favorable for spray applications, use granule formulations. Because granules are generally on a dense carrier, they are not subject to drift. However, when using granules, avoid applications to sidewalks or driveways where rain or irrigation can increase run off. Finally, take care in the placement of insecticide applications and avoid broadcast applications when a more targeted application will provide the same level of control.

A new controlled release SC formulation of deltamethrin (Suspend PolyZone) was recently introduced by Bayer. In this formulation, the AI is protected from mechanical abrasion and washoff by rainfall or irrigation. This helps keep the insecticide where it is applied, reducing runoff.
 

9. Will there be a problem with visible residues on treated surfaces?

Unsightly visible residues on treated surfaces may occur following application of spray treatments. This problem is most common when using WP formulations at high labeled rates and spray volumes. The visible residue is primarily due to the carrier (e.g. talc, clay) used in the WP formulation. Visible residues appear to be more of a problem on indoor surfaces. When making residual insecticide applications indoors, use EC, SC or CS formulations to minimize the risk of leaving behind a visible residue.
 

10. Are there regulatory issues that limit product use?

ALWAYS READ THE ENTIRE LABEL BEFORE USING A PRODUCT AND FOLLOW ALL LABEL DIRECTIONS. If you are not sure about the use of a certain product, check with local regulatory officials, product manufacturers, distributors or others that can provide clear and accurate information about the product.

After reviewing these questions, it should be apparent that no one formulation will work best for every situation. A professional who consistently uses multiple formulations during a day’s work is taking these questions into account and is more likely to achieve effective results. Take time to inspect and gather important information about the site before making insecticide applications.